The present invention relates to radio signal separation systems and more particularly to signal separation systems which can separate a plurality of signals from any arbitrary group of signals received by an antenna system.
Existing signal nulling systems that have been developed include the interference cancellation system for eliminating interference in radio receivers as found in U.S. Pat. No. 3,669,444 to the present inventors R. N. Ghose and Walter Sauter. The interference cancellation system of the aforementioned patent allows simultaneous transmit and receive on the same radio frequency from adjacent antennas without interference. In that system, it was necessary to cancel out the unwanted transmitter signal from the received signal and, hence, allow full duplex radio transmissions on a single frequency or any adjacent frequencies. Briefly, employing the system of U.S. Pat. No. 3,669,444, when it is connected in the line between the radio receiver and its antenna, the system will sense the interferring signal and generate a signal which is the negative compliment of the interferring signal. The negative compliment signal is added to the radio receiver antenna line to cancel out the interferring signal.
The above described interference cancellation system uses signal controllers as part of the signal separation system. Prior art known to the applicants disclosing signal controllers include U.S. Pat. No. 4,016,516 to W. Sauter and U.S. Pat. No. 3,648,176 to D. Martin. The signal controller disclosed in the aforementioned Sauter 516 patent uses semiconductors and is designed to be inserted into an RF transmission line to control the signal amplitude ratio and polarity by an external DC voltage control means. U.S. Pat. No. 3,648,176 discloses a signal controller to cancel out unwanted signals by employing an RF potientiometer directly coupled to a drive motor and a velocity generator whereby corrections in potentiometer ratios may be made automatically by driving the motor via a feedback loop.
None of the foregoing art references are able to separate out more than one signal from a group of individual signals received by an antenna system. Consequently, a need continued to exist for a signal separation system which can separate a number of individual signals from external interferences and from each other.